KDE 4.1 has some issues with older Nvidia cards (pre-5000 series), so that's one problem. Also *buntu 8.10 has a new version of X.org that is giving people some challenges. Here's the 8.10 release notes -- you can see whether any of those issues are behind your Compiz problem:

The only thing I've noticed on mine is that the KDM login GUI does not always run automatically on boot. Half the time it dumps me to the CLI and I have to log in there and run "startx". But then it starts every time -- it might be due to overclocking or something like that.

I just saw this thread and thought i would show off some
screenshots. Running a custom Gentoo install, kde3 and 4
and, Compiz-Fusion. For those of you interested in checking
out Compiz-Fusion without doing a linux install. You can dl
the Sabayon Linux LiveDVD. It comes with all the different
video drivers already installed and Compiz-Fusion. Sabayon
is a Gentoo based distro. For those of you with ATI or Intel
video cards i would recommend Ubuntu/Kubuntu. ATI and
Intel both have Open Source drivers and Ubuntu comes
with Compiz-Fusion already installed 'it just needs to be
activated' and, is very user friendly.

Anyhow here are a couple of screenshots. First is the Cube transformed
into a Cylinder and the second is the Cube transformed into a Sphere.